Record reproduction circuit



Nov. 12, 1946.

W. R. KOCH RECORD REPRODUCTION CIRCUIT Original Filed 0c t. 6, 1942 2 Sheets-Sheet 1 0567114701? D/SCR/Ml/V/ITOR AMPLIFIER DETECTOR vvvvv' 0/SCR/M/M470R E RM OSC'IZZATOI? 70 PICK UP r0 400/0 cmcu/p INVENTORQ W/A/F/ELD R. KOCH IIBY ATTORNEY Nov. 12, E946.

w. R. KOCH RECORD REPRODUCTION CIRCUIT Original Filed Oct. 6, 1942 2 Sheets-Sheet 2 70 4017/0 C/RCl/l iMosc/uhroa DETECTOR 70 P/CK UP .INVENTOR.

WM/F/ELD R. KOCH BY ATTORNEY Patented Nov. 12, 1946 7 'Winfield R. Kojch, Iiiaddonfield, N. 11., assignor to Radio Corporation of America, a corporation of Delaware Original application October 6, 1942, Serial No. 460,940, now Patent No. 2,361,634, dated'OctOber 31,1944. Divided and this application September 16, 1943, Serial No. 502,589

12 Claims- My present invention relates generally .to phonograph record reproduction circuits, and more especially to circuits of thegeneral type utilizing a frequency modulation oscillator having a capacity pickup. This application is a division of my application Serial No. 460,940, filed October 6, 1942, now Patent No. 2,361,634, granted October 31, 1944.

C. M. Sinnett has disclosed in his application Serial No. 459,375, filed September 23, 1942, a system for reproducing phonograph records with high fidelity and high gain, but with minimum production cost. In general, the system comprises a capacity pickup device capable of converting recorded sound waves into frequency modulated high frequency waves, a discriminator-rectifier network being used to derive from the modulated waves the original audio signals which had been recorded. The system has other uses. Microphones and pressure-responsive pickups can be employed as the input devices. 7

One of the main objects of my invention is to provide various improved circuits of the same general type, but wherein sensitivity, fidelity and economy are extended to a further "degree.

The novel features which I believe to be 2 o to be associated with the stylus of capacity pickup I is not shown, and the latter is schematically represented as consisting of a pair of spaced metal plates. However, it should be "clearly understood that thepickup device I may be replaced by any variable reactance device, such as a microphone or pressure-responsive element. The stylus plate (usually a ribbon) is connected-to the grounded sheath of the high impedance .coaxial cable 2. The immobile plate is connected to the inner conductor; the latter is connected to the high alternatingpotntial side of the'os'cillator tank circuit.

The oscillator tube 3 may be a GSA? 'typetube whose cathode is returned to an intermediate point on the adjustable inductance coil 4. The latter is schematically represented as being of the powdered-iron core type; condenser 5 shunt v the coil to resonate the same to the mean, or center, frequency of the oscillator.

. up I and capacity of cable 2 and condenser 5 provide the normal resonating capacity for the coil 4. The first grid 6 is connected backitothe high alternating potential side of .coil dby'the characteristic of my invention are set forth with particularity in the appended claims; the invention itself, however, as to both its organization and method of operation will best be understood by reference to the following description taken in connection with the drawings, in which I have indicated diagrammatically several circuit organizations whereby my invention may be carried into effect.

In the drawings:

Fig. 1 shows an embodiment of the invention, wherein the modulated wave energy across the discriminator is greatly increased,

Fig. 2 shows a modification wherein an andplifier of the modulated waves is concurrently used as a detector, j

Fig. 3 is a modification of the circuit-of Fig. 2, the oscillator functioning simultaneously as a rectifier,

Fig. 4 is an embodiment wherein the detector is of the multi-grid type,

Fig. 5 is a variation of the-circuit of Fig. 4, the oscillator acting as a, detector.

Referring now to the accompanying drawings,

wherein like reference .charactersin the different figures designate similar circuit elements, it will be understood that the systems disclosedherein aregenerally of the type describedand claimed in the aforesaid Sinnett application. The record of the latter through the record grooves.

usual blocking condenser I, and grid return resistor 8 connects the grid 6 to ground. The second, third and fourth grids are tied together to function as an effective single electrode, and are supplied with approximately volts thereby providing a positive oscillator anode which is designated by numeral 9. a

Circuit 5- 4 has a normal or mean frequency which is varied by changes in capacitance of the pickup. The capacitance changes occur by virtue of motion of the stylus produced. by the riding As a result-of the capacitance variations of pickup I, the frequency of the oscillator tank circuit will be varied. The frequency deviation relative to the mean frequency may extend to any desired frequency value. For example, an overall frequency deviation of 30 kilocy'cles (kc) may-be employed. The mean frequency can be of the order of 30 megacycles (mc.). These are purely illustrative values. a

The frequency modulated (FM hereinafter for brevity) high frequency oscillations appear-in the circuit connected'to plate i9 by virtue 'of electron coupling between the oscillator section of tube 3 and plate It. :The' electron coupling phenomenonis well known, and it is sufficient for the purposes of this application to point out that the FM signal energy appearing in the plate circuit of tube-3 is amplified. Asecond-tube is provided, and this tube is designated by numeral In general, the pick- The tube may be one of the pentode-diode type wherein there is an electrode 2 functioning as a diode anode. The anode I2 is adjacent cathode l3 which is grounded. The pentode section of the tube comprises the cathode l3, plate l4 and three intermediate grids designated l5, l6 and IT.

The intermediate, or screen, grid I6 is connected to the source of potential of oscillator anode 9, the connection between these electrodes being bypassed to ground by condenser l8 for high frequency currents. The control grid I is coupled to the high potential side of the oscillator tank circuit by coupling condenser l9, resistor returning grid l5 to ground. Plates l0 and M are connected in common to a point of approximately +200 volts through the coil 2| of the discriminator circuit. This coil 2| is schematically represented as having a powdered iron core. vides a resonant circuit.

The core of coil 2| is adjusted so that the discriminator circuit 2|-22 has a single peak resonance curve. The peak frequency is either above or below the mean, or center, frequency of the FM signals. By way of illustration, the center frequency may be located at an intermediate point of either slope of the resonance curve of circuit 2|-22. It is desirable to have these slopes as linear as possible. Hence, it is seen that discrimination occurs, and that the FM signal energy developed across the plate circuit of the oscillator is transformed at circuit 2|- 22 into corresponding amplitude modulated wave energy. The frequency deviations of the FM signals correspond to the sound waves of the phonograph record, and the corresponding amplitude modulated wave energy similarly corresponds to the recorded sound waves.

The amplitude modulated wave energy is rectified bythe diode |2--|3. Anode I2 is coupled by condenser 23 to the high potential side of coil 2|. The modulation voltage is developed across a load resistor 24 arranged in series with the radio frequency choke coil 25 between anode l2 and ground. The high frequency bypass condenser 26 shunts resistor 24. The modulation signals derived from resistor 24 may be transmitted to any form of audio utilizing circuit.

By using the pentode-diode tube II it is possible to have the pentode section in parallel with the amplifier part of the oscillator tube 3. The radio frequency voltage is thereby increased across discriminator circuit 2|22 to a value of over double the magnitude that would be secured by feeding the diode directly from the plate of the oscillator. In this way sufficient audio frequency voltage is derived from a simple diode rectifier to operate the audio frequency amplifier. The circuit is free from possible noises which would ordinarily be introduced in a voltage-doubler diode circuit through leakage. Because of the high frequencies employed, short leads are desirable. By giving grid resistor 20 a value of about 40,000 ohms the grid is driven further positive, and considerably more radio frequency output voltage is obtained across the discriminator circuit. The choke coil 25 affects the Q of the discriminator very little. In general, then, it will be seen that in the circuit of Fig. 1 the FM signal energy is fed into the discriminator circuit by electron coupling in tube 3, and is concurrently transmitted from tube II by the amplifier action of the pentode section of tube I In the arrangement of Fig. 2, the plate III of The condenser 22 shunts coil 2|, and prooscillator tube 3 is connected to the positive voltage source Which feeds the oscillator anode 9 and the screen grids of the following amplifier tube. Otherwise, the oscillator circuit of Fig. 2 is similar to that shown in Fig. 1. The amplifier tube is a pentagrid tube, and nay be of the GSA? type. The tube is designated by numeral 30, and its cathode 3| is connected to an intermediate point on the coil 2| of discriminator circuit 2|-22. In this modification the high potential side of the discriminator circuit is connected to the plate 32 of tube 30 by the coupling condenser 33, while the low potential side of the discriminator circuit is grounded. The choke coil 25 and series load resistor 24 are arranged between plate 32 and ound.

The control grid 34 of tube 30 is coupled, as in Fig. 1, to the high alternating potential side of oscillator circuit 45. It will be noted that the second, third and fourth grids of tube 30 are tied together, and effectively function as a common screen electrode. The cathode 3| and plate 32 of tube 30 cooperate to provide diode rectification. It will be noted that the discriminator circuit 2|22 is arranged in the cathode circuit of tube 30. This is very similar to the oscillator circuit used, except that in the oscillator the control grid is affected from its own cathode circuit instead of from an external source of voltage as in the case of amplifier operation. The voltage gain is all supplied by the step-up secured from the tuned circuit 2 |-22. The discriminator circuit is, of course, slightly mistuned as in the case of Fig. 1, so as to secure an amplitude variation corresponding to the frequency deviation introduced by the capacity change in the pickup device.

In Fig. 2, the plate current of tube 3 does not feed directly into the discriminator circuit 2 |22. The oscillator voltage is applied to the control grid 34 of tube 30 from the high potential side of circuit 4-5. The tube 30 acts as a cathode follower amplifier. The output voltage of tube 30 is stepped up and shifted in phase because of the tapping point of cathode 3| on coil 2|. The

said output voltage is applied to the plate 32 of tube 30. The plate 32 cooperates with cathode 3| to provide a rectifier, and in this respect is similar to diode |3|2 of Fig. 1. However, the rectifier of Fig. 2 is grid-controlled. The rectifier path between cathode 3| and plate 32 is controlled in phase with the voltage of grid 34.

The detector of Fig. 2, therefore, is a grid-controlled rectifier. When grid 34 is positive relative to cathode 3| space current flows through the tube, and diode rectification can take place.

When grid 34 is negative no space current flows.

Rectification by 3|-32 cannot take place. Be-

cause of the phase shift between the voltage ap- 0 plied to grid 34 and that applied to plate 32 (which changes in accordance with the change in oscillator frequency) the output voltage across resistor 24 contains audio frequency currents,

Each of Figs. 2, 3, 4 and 5 employs the passive discriminator circuit 2|-22 in the cathode lead of the amplifier tube. The difference in these four circuits is in the manner of securing detection of the resulting amplitude-modulated wave energy. Because of the slight mistuning there is also present a difference in phase of the oscillator and discriminator circuit voltages, which varies when the frequency is varied. This is utilized in the detector circuits to give a greater output than would be secured by depending on amplitude variations alone. This action is ex- 'plained asfollows: Whenthe grid of eitherthe oscillator or amplifier tubes is driven extremely farfthe plate current will flow in the tube only for short intervals during the extreme positive operation of the radio frequency voltage. When there exists a phase difference between these impulses of current arriving at the anode and the voltage'applied to theanode by the discriminator circuit, only during a short period can this plate current flow. If the phase of the voltage difiers sufliciently then no plate current can flow. If it is in phase with the current, the maximum plate current can flow. Variation of the oscillator frequency will cause plate current to vary be- "tween-these extremes. By using the voltage drop across the series resistor the audio frequency output voltage can be secured.

Referring now to Fig. 3, it is-pointed out that in this modification the'plate l acts as the anode 'functions'as the anode of a grid-controlled rectifier of the amplitude modulated wave energy developed by the discriminator circuit 2 i22. It is, again,emphasized that by virtue of the phase shift noted above, sharper discrimination is secured. The variation in voltage applied to plate In, because of the selectivity of the discriminator circuit, is accompanied by a change in phase thereby enhancing the rectifier output variation responsive to frequency change.

In Figs. 4 and 5, rectificationissecured by a multi-grid detector. In the modification of Fig.

4, the plate H] of oscillator tube .3 is connected to the tied grids 9. The detector tube is designated by numeral 40, and may be a pentagrid tube of the GSA? type. The control grid 34 is connected to the oscillator grid of tube 3. second and fourth grids of tube 40, designated by numerals il and 42 respectively, are connected to the plate is and grids 9. The control grid 43, located between grids ll and 42, is connected to ground by a resistor M, and condenser 45 couples the grid to the high potential side of the discriminator circuit. The plate 32 of tube 40 provides the audio voltage across 'the output load resistor 50, and the lower end of resistor 50 is connected to a source of positive potential. The load resistor 50 is shunted to ground by the high frequency bypass condenser 5|. In Fig. 4, as the frequency of the oscillations changes, the phase of the voltage applied to grid 43 will vary from that applied to grid 34. If the oscillator frequency changes enough to produce resonance of the discriminator circuit, the two grid voltages will be in phase and maximum plate current will flow. By limiting the swing to one side of the discriminator, the plate current will vary from this maximum to a lowvalue. Both grids are, of course, supplied with sufficient voltage so that the tube is operated on a non-linear portion of its characteristic. Tube it, in this modification, acts as a cathode follower amplifier. A voltage from the oscillator tank circuit 5-4 is applied to grid 34. The stepped-up and phase-shifted voltage is applied togrid 43. The Variable phase between the alternating voltages impressed on grids The' 1 audio frequency voltage.

34 and 43 yields a plate current containing-the audio frequency components.

I Thearrangement of Fig. 5 differs from'that shown in Fig. 4 in that the oscillator tube 3 is givenithe additional function of acting as the multi-grid detector which was described in connection with Fig. 4. This is accomplished by having the second and fourth grids of tube 3 acting asthe oscillator anode 9, while the intermediate grid!) is connected by lead 60 to the junction of condenser 45 and resistor 44. The plate of tube to is tied to the second, third and fourth grids of-the tube, and have in common a positive'potential applied thereto. The plate ll] of the oscillator'tube 3 isconnected to the load resistor 50 across which latter resistor is "developed the In Fig. 5, the amplifier tube 40 acts as a cathode follower amplifier. The stepped-up and phase-shifted voltage 'developedacross 2!-22 is applied to grid 9' of the tube 3. The variable phase between the voltages applied to the first and thirdgrids of tube '3 causes the plate current of tube 3 .to vary accordingly.

In this way there is secured across the load resistor 50 plate current having audio frequency components.

The circuits shown in Figs. 2, 3, 4 and5 have the advantage of employing standard commercial types of tubes, and only volts of +B supply is required. It should, also, be noted that the pair of tubes required in these circuits can be of the same type, thereby simplifying manufacture and servicing. The tubes used (6SA'7) have helical heaters thereby reducing any hum modulation. If desired, in Figs. 4 and 5 the plate resistor 50 may be returned to ground, instead of to-the positive potential point.

While I have indicated and described several systems for carrying my invention into effect,

it will be apparent to one skilled in the art that my invention is by no means limited to the particular organizations shown and described, but

that many modifications may be made without departing from the scope of my invention, as set forth in the appended claims.

What I claim is:

1. In combination, a tube provided with an oscillator section and a postive output electrode,

means connected to said oscillator section to provide angular velocity-modulated oscillations which have a predetermined mean frequency, electron coupling between said oscillator section and said output electrode developing said angular velocity-modulated oscillations in the output electrode circuit, a resonant circuit connected to said output electrode, said resonant circuit being tuned to a frequency suiiiciently different velocity-modulated oscillations in the output electrode circuit, a resonant circuit connected to said output electrode, said resonant circuit being tuned to a frequency suificiently different from said mean frequency to permit the resonant cirv and said output electrode developing said angular velocity-modulated oscillations in the output electrode circuit, a resonant circuit connected to said output electrode, said resonant circuit being tuned to a frequency sufficiently different from said mean frequency to permit the resonant circuit to function as a discriminator circuit, an electron discharge device having an input electrode coupled to said oscillator section, said device having an output electrode coupled to said discriminator circuit, said last named electron discharge device including at least a cathode having said discriminator circuit in the space current path thereof.

4. In combination, a tube provided with an oscillator section and a positive output electrode, means connected to said oscillator section to provide angular velocity-modulated oscillations which have a predetermined mean frequency, electron coupling between said oscillator section and said output electrode developing said angular velocity-modulated oscillations in the output electrode circuit, a resonant circuit connected to said output electrode, said resonant circuit being tuned to a frequency sufficiently different from said mean frequency to permit the resonant circuit to function as a discriminator circuit, an electron discharge device having an input electrode coupled to said oscillator section, said device having an output electrode coupled to said discriminator circuit, the output electrode of said first mentioned tube and the cathode of said electron discharge device functioning as a rectifier to rectify amplitude modulated wave energy appearing across said discriminator circuit.

5. In combination, a tube provided with an oscillator section and a positive output electrode, means coupled to said oscillator section to provide angular velocity-modulated oscillations which have a predetermined mean frequency, electron coupling between said oscillator section and said output electrode developing said angular velocity-modulated oscillations in the output electrode circuit, a resonant circuit connected to said output electrode, said resonant circuit being tuned to a frequency sufliciently different from said mean frequency to permit the resonant circuit to function as a discriminator circuit, an amplifier tube separate from the first tube having an input electrode coupled to said oscillator section, said tube having an output electrode coupled to said discriminator circuit.

6. In combination, a tube provided with an oscillator section and a positive output electrode, means coupled to said oscillator section to provide angular velocity-modulated oscillations which have a predetermined mean frequency, electron coupling between said oscillator section and said output electrode developing said angular velocitymodulated oscillations in the output electrode circuit, a resonant circuit connected to said output electrode, an electron discharge device having an input electrode coupled to said oscillator section, said device having an output electrode coupled to said resonant circuit, and a rectifier coupled to said resonant circuit for developing modulation voltage.

7. In combination, a tube provided with an oscillator section and a positive output electrode, means coupled to said oscillator section to provide angular velocity-modulated oscillations which have a predetermined mean frequency, electron coupling between said oscillator section and said output electrode developing said angular velocity-modulated oscillations in the output electrode circuit, a resonant circuit connected to said output electrode, said resonant circuit acting as a discriminator circuit, an electron discharge device having an input electrode coupled to said oscillator section, said device having an output electrode coupled to said discriminator circuit, said last named electron discharge device including at least a cathode having said discriminator circuit in the space current path thereof.

8. In combination, a tube provided with an oscillator section and a positive output electrode, means connected to said oscillator section to provide angular velocity-modulated oscillations which have a predetermined mean frequency, electron coupling between said oscillator section and said output electrode developing said angular velocity-modulated oscillations in the output electrode circuit, a resonant circuit connected to said output electrode, said resonant circuit being tuned to a frequency sufliciently diiferent from said mean frequency to permit the resonant circuit to function as a discriminator circuit, an electron discharge device having an input electrode coupled to said oscillator section, said device having an output electrode coupled to said discriminator circuit, the output electrode of said first mentioned tube and the cathode of said electron discharge device functioning as a rectifier to rectify amplitude modulated Wave energy appearing across said discriminator circuit, and the discriminator circuit being in the space current path of said device.

9. In combination with an oscillator of variable frequency, an electron discharge tube having at .least a cathode, control grid and anode, means cathode and anode to provide a rectifier circuit,

and said grid controlling the space current between the cathode and anode.

10. In combination with a tuned circuit having a frequency-varying element connected thereto, an electron discharge tube having at least a cathode, grid and anode electrode operatively associated with the tuned circuit to provid an oscillatory circuit of variable frequency, a second electron discharge device having at least a cathode, control grid and positive cold electrode, means supplying oscillatory voltage from the tuned circuit to said second device control grid, a frequency discriminator circuit connected in the space current path of the second device and adapted to be traversed by the space current of the second device, means connecting the cathode of said second device to an intermediate potential point on the discriminator circuit, and a resistive load in circuit with the discriminator circuit 9 across which is developed detected voltages rom currents flowing through the discriminator circuit.

11. In a record reproducer system, a tube provided with oscillator electrodes, means connected to the oscillator electrodes to provide angular velocity-modulated oscillations which have a desired mean frequency, a frequency discriminator circuit, an electron discharge tube having said discriminator circuit directly connected in its space current path whereby the space current of the last mentioned tube flows through said discriminator circuit, a resistive load in circuit with said discriminator circuit across which is developed detected voltages from currents flowing 1 through the discriminator circuit, and means reto said oscillations for controlling the space cur-.

rent path of the second tube and rectifier means including the anode and cathode of the second tube to derive modulation signal voltages from said space current path.

WINFIELD R. KOCH. 

